An Extended Grid of Nova Models. Iii. Very Luminous, Red Novae

Abstract

Extremely luminous, red eruptive variables like RV in M31 are being suggested as exemplars of a new class of astrophysical object. Our greatly extended series of nova simulations shows that classical nova models can produce very red, luminous eruptions. In a poorly studied corner of 3-D nova parameter space (very cold, low-mass white dwarfs, accreting at very low rates) we find bona fide classical novae that are very luminous and red because they eject very slowly moving, massive envelopes. A crucial prediction of these nova models -in contrast to the predictions of merging star ("mergeburst") models -is that a hot remnant, the underlying white dwarf, will emerge after the massive ejected envelope has expanded enough to become optically thin. This blue remnant must fade on a timescale of decades -much faster than a "mergeburst", which must fade on timescales of millenia or longer. Furthermore, the cooling nova white dwarf and its expanding ejecta must become redder in the years after eruption, while a contracting mergeburst must become hotter and bluer. We predict that red novae will always brighten to L ∼ 1000L ⊙ for about 1 year before rising to maximum luminosity at L ∼ 10 6 − 10 7 L ⊙ . The maximum luminosity attainable by a nova is likely to be L ∼ 10 7 L ⊙ , corresponding to M ∼ −12. In an accompanying paper we describe a fading, luminous blue candidate for the remnant of M31-RV; it is observed with HST to be compatible only with the nova model.

V1309 Scorpii: merger of a contact binary

“…Several interpretations of the eruptions were proposed. They include an unusual classical nova (Iben & Tutukov 1992;Shara et al 2010), a late He-shell flash (Lawlor 2005), or a thermonuclear shell flash in an evolved massive star (Munari et al 2005). presented numerous arguments against these mechanisms.…”

Nucleosynthesis in Novae

“…Typical accreted envelope masses range between 10 -3 -10 -7 M sun . Detailed hydrodynamic simulations [10][11][12][13][14] have revealed the influence of the mass-accretion rate on the properties of the outbursts. Indeed, high mass-accretion rates result in more energy released from gravitational compression of the envelope, and hence, times to reach ignition conditions are reduced.…”

“…For instance, Yaron et al [14] reported mass ejection from models of 1 M sun white dwarfs accreting solar-like material at a rate as high as 10 -7 M sun yr -1 (see ref. [12] for models of very luminous white dwarfs). It is also worth noting that Yaron et al have computed nova models with very low mass-accretion rates, 5×10 -13 M sun yr -1 .…”

“…As a result of the longer accretion phase, larger masses, and hence, larger pressures are achieved, which translate into more violent outbursts (similar effects have been described elsewhere; see, for instance, refs. [11][12][13][14]17]). On the other hand, in hot, luminous white dwarfs the outermost core layers become convective, and larger levels of mixing through the core-envelope interface are found.…”

The unreasonable effectiveness of experiments in constraining nova nucleosynthesis

“…[5][6][7][8][9][10][11]). The underlying assumption in these models is, obviously, spherical symmetry, where the explosion is modeled as occurring uniformly and simultaneously over spherical shells.…”